The present technology relates to a submount used to assemble a semiconductor light-emitting element, a submount assembly using the submount, and a submount assembling method.
Recently, for researches in a leading-edge science region using laser light of pulse duration in the attosecond range or the femtosecond range, ultrashort-pulse/ultrahigh-power lasers have been frequently used. Moreover, in addition to scientific interest in an ultrafast phenomenon on a timescale of picoseconds or femtoseconds, applied research in ultrashort pulse lasers with use of high peak power for practical use such as microfabrication or two-photon imaging has been actively conducted. Further, a high-power/ultrashort-pulse laser diode element with a light emission wavelength of 405 nm made of a GaN-based compound semiconductor is expected to serve as a light source of a volumetric optical disk system which is expected as a next-generation optical disk system following a Blu-ray optical disk system, a light source necessary in the medical field, the bio-imaging field, or the like, or a coherent light source covering an entire visible light range.
As the ultrashort-pulse/ultrahigh-power laser, for example, a titanium/sapphire laser is known; however, the titanium/sapphire laser is an expensive and large solid laser light source, which is a main impediment to the spread of the technology. If the ultrashort-pulse/ultrahigh-power laser is realized through the use of a laser diode or a laser diode element, it is considered that a large reduction in size, price, and power consumption of the ultrashort-pulse/ultrahigh-power laser, and high stability of the ultrashort-pulse/ultrahigh-power laser will be achieved, thereby leading to a breakthrough in promoting widespread use of the ultrashort-pulse/ultrahigh-power laser in these fields.
A laser diode device assembly with an all-semiconductor structure as such a 405-nm-wavelength high-peak-power picosecond-pulse light source typically has an MOPA (Master Oscillator and Power Amplifier) configuration. More specifically, the laser diode device assembly is configured of a laser diode generating a picosecond pulse, and a semiconductor optical amplifier (SOA, semiconductor laser amplifier) amplifying the generated picosecond pulse. Herein, the optical amplifier directly amplifies an optical signal itself without converting the optical signal into an electrical signal, and has a laser structure without a resonator, and amplifies incident light by an optical gain of the amplifier. More specifically, one of pulse light sources with the MOPA configuration generating a picosecond pulse is a mode-locked laser diode device assembly including an external resonator.
The semiconductor optical amplifier is achievable by reducing reflectivity of both end surfaces of a laser diode element. To reduce reflectivity, a technique of applying nonreflective coatings configured of a dielectric multilayer film to the end surfaces is typically performed; however, even though the nonreflective coatings are applied to the end surfaces of the laser diode element including a waveguide perpendicular to the end surfaces, residual reflectivity is still high, and it is difficult to achieve a semiconductor optical amplifier having a sufficient optical gain. Therefore, a technique of reducing effective reflectivity is used in a semiconductor optical amplifier including a waveguide arranged to be inclined with respect to the end surfaces, i.e., an oblique waveguide. Moreover, in the case where it is desired to reduce the reflectivity of the end surfaces of the laser diode element as in the case of a mode-locked laser diode element assembly configured with use of an external mirror, it is also effective to adopt a technique of arranging the waveguide to be inclined with respect to the end surfaces, that is, to adopt a laser diode element including an oblique waveguide.
In the case where the laser diode element or the semiconductor optical amplifier (hereinafter collectively referred to as “semiconductor light-emitting element”) is actually used, it is necessary to efficiently optically couple the semiconductor light-emitting element to a lens, an optical device, an optical element, or another device. However, as described above, when the semiconductor light-emitting element with the waveguide inclined with respect to the end surfaces of the semiconductor light-emitting element is mounted to allow an axis line thereof to be parallel to an optical axis of a system, by Snell's law, light emitted from the semiconductor light-emitting element is inclined at a certain angle with respect to the optical axis of the system. Therefore, there is an issue that a system in related art is not allowed to be used without change. Moreover, in the semiconductor optical amplifier, there is an issue that optical coupling efficiency of incident light declines.
Therefore, as a method of solving such issues, Japanese Unexamined Patent Application Publication No. 2007-088320 discloses a technique of inclining a mount section of a heat sink, and Japanese Unexamined Patent Application Publication No. H11-087840 discloses a technique of forming markers 17 and 18 on a p-side contact layer of a laser diode element.